Study On Characteristic Of Electric Power Steering System Model Integrating The Function Of Active Steering

With the advanced technology of intelligent control, LSI and vehicle networkingrapid development, electronic control system has become a hot issue in the field ofcontemporary research, which improves vehicle safety, operational stability and ridingcomfort for the target. Function mechanisms and control characteristics of the newelectric power steering system integration active steering function are studied. So, itbrings into full play the functions and adjustment range of each steering system. Beside,driving stability and active safety can be improved in some extreme conditions such asthe separation of road, large lateral forces and cornering brake.With Dr. Foundation of Chongqing Jiao Tong University (Grant No.:100982) andEducation and Research Foundation of Chong-Qing (Grant No.:12JK0693) which iscalled "control mechanism and key technologies of new electric power steering systemintegration active steering are reached". The new electric power steering systemintegration active steering function is overall designed on the basis of the relevantresearch status at home and abroad. The variable gear ratio characteristics oftransmission and the control features of assist angle motor are studied. The mainresearch works include the following aspects:First of all, in order to bring into full play the functions and adjustment range ofsteering system, a new type of EPS system integration active steering function isdesigned by research and analysis driving mechanism and working principle of EPS andAFS. According to the driver’s intention and vehicle conditions, the new EPS systemcan make active steering or steering compensation. The power from assisted motor isapplied by reference torque and vehicle driving conditions. By adjusting front wheeladditional angle real-time and changing steering ratio of initiative corner motor, thehandling and stability of vehicle are improved. Meanwhile, the designed for assemblyof the new EPS system integration active steering function is made based onthree-dimensional software.Then, the gear ratio is changed with speed in the active front steering system. Thedouble planetary gear dynamics model of new EPS system is established. The idealnonlinear variable transmission ratio curve of AFS based on vehicle steady-stateresponse is established, which uses the method of given system yaw rate gain value.The transmission ratio curve by simulation is proved to be reasonable. The double loop cascade PID control strategy with current loop and position is designed based on assistangle motor. The simulation results show that the response characteristics of the motortorque and output current are improved significantly under un-load and load conditions.The system dynamics models and simulation models are built by analysis thestructure of EPS and dynamics characteristics. According to the assist principles, theideal power characteristic curve is designed. NCD Blockset optimization toolbox isused to optimize the initial parameters of the adaptive controller. In addition to, theclosed-loop tracking control simulation is done to the target current by using adaptivefuzzy PID control strategy. Comparing the simulation results of the target currentresponse speed, the motor output torque, steering bogie yaw rate and some otherperformance parameters, a conclusion can be made that the control strategy can improvethe responsiveness and tracking of electric power steering control system and improvethe steering performance and operational stability of vehicles. The effectiveness ofnon-linear changes ratio curve is demonstrated by using the control method of anadditional front-wheel angle.The last but not least, the new EPS system based on vehicle handling and stabilitycontrol is studied by using H∞robust control strategies on control features of a newelectric power steering system integration active steering function. Basing on a vehiclehandling dynamics model with EPS, the EPS robust controller merging active steeringfunction is designed, which take the steering light and sensitivity, return to centercharacteristics and vehicle handling and stability as evaluation to put out. Then, asimulation is carried out on it. Simulation results show that the EPS control systemmerging active steering function not only achieve the control characteristics oftraditional EPS, but can provide the active steering function in extreme conditions toimplement the requirements of the vehicle handling and stability. So the maximizeadjustment range can be achieved for the new EPS.